This ear canal 10, as illustrated in FIG. 1 in the coronal view, is generally narrow and tortuous and is approximately 26 millimeters (mm) long from the canal aperture 11 to the tympanic membrane 15 (eardrum). The lateral part 12 is referred to as the cartilaginous canal due to the underlying cartilaginous tissue 16 beneath the skin 14. The medial part, proximal to the tympanic membrane 15, is rigid and referred to as the bony region 13 due to the underlying bone tissue 17. A characteristic first bend occurs roughly at the aperture 11 (FIG. 2) of the ear canal. A second characteristic bend occurs roughly at the bony-cartilaginous junction 8 and separates the cartilaginous region 12 and the bony region 13. The two bends inside the ear canal define a characteristic “S” shape (FIG. 2). The ear canal 10 is generally hidden from view (front and side) behind a backward projecting eminence known as the tragus 3 (FIGS. 2-4). The ear canal is also hidden from view from the back by the presence of the pinna 4 (also referred to as auricle). The dimensions and contours of the ear canal 10 vary significantly among individuals.
The lateral part of the external ear, represented by the ear canal 10, tragus 3, pinna 4 and concha cavity 5, generally comprises flexible cartilaginous tissue that moves in response to pressure, including the motion of the mandible 7 (jaw bone, FIG. 3). Anterior of the ear canal 10 and the tragus 3 regions is the temporomandibular joint region 20, defined by the condyle 6 (upper part of the mandible 7) articulating with the temporal bone 18 (part of the cranium). The temporomandibular joint region 20 (alternatively referred to herein as the condyle region) is generally anterior to the tragus 3 and not considered part of the ear anatomy, nor related to the human hearing physiology. Similar to the general structure of the ear, the cartilaginous tissue 16 separates the condyle 6 from the ear canal cavity 10 as shown in FIG. 2.
Placement of a hearing device inside the ear canal 10 is generally desirable for various electroacoustic advantages such as reduction of the acoustic occlusion effect, improved energy efficiency, reduced distortion, reduced receiver vibrations, and improved high frequency response. Canal placement may also be desirable for cosmetic reasons since the majority of the hearing impaired may prefer to wear an inconspicuous hearing device. A canal hearing device can be inserted entirely or partially inside the ear canal. In the context of this application, any hearing device inserted inside the ear canal, whether partially or completely, may be referred to as a canal hearing device. This includes what is known in the hearing aid industry as Completely In the Canal (CIC), In-The-Canal (ITC), and extended wear deep canal invisible types.